Electromagnetic transmitter and receiver



M, 1936. A. A. THOMAS ELECTROMAGNETIC TRANSMITTER ANb RECEIVER Filed Feb. 10, 1928 R O N E V m Patented Oct. 14, 1930 ome mm; r;

This invention is: for an'iele'ctromagnetic v translating; device I of: novel construction andva improved opera'tion' for converting m'echim ical motion into electric impulses or causing electric impulses ti) produce mechanical inotion. The uses of my invention are varidus; as for telephone receivers andtransrnitters," phbnograph recdrding and reprodncinginsbrnm'en'ts, and for other devices along si'm ilax lines. invention 'is eon'stpucted i in the form 6f a phonogrziiph pickup;v it 1 is particularly usefuljin'playifig finely 'grobved vertical-Rent recdrds; like those, of the Edison tyfifallthiflgh it is equal y jeiiici'ent pi' 1st an acoustic diaphragm, recdrding tool; "a.

reproducing-a tyl s, and 7 the like, c5111;

melil' fed dir cclyjon' the spring' rmatiir'e; $6

an thaw d lic e yib e 'iqes dim s, srnitted from 'one' v tcjtheyo'thei "wit hpl p' t li'eippsisibility of lost motion, j

epreferred form of myj inizeiifioii the nx eti s. be si t b fla m jw el ef spri g bent into ja n ppen elliptic .or pval shapewwith its'endscitending'toward each Other andttw ssl to .tl em t r l fl e i g e pnoduces, an aringtnre struc ture with a mfi i z c us 'i rt 'ef resili h y c ppo ted nl ehfsi n coll ia qn ba s n.c ir eo ze 'clpw-v IiQ l 11 ano her :form 9 y v ti n, the4 armature is a magnetic ribbqn connected at its endsbo the o ut'er poles of ;& threer-pole mag;v

net andsorconstructed as to be constantlyrtem sinned-0r stretched,-as by means of transverse c0rrugationsw Both forms cfarmat'ure are;

ekceedingly sensitivewand lciipable 0f reproducing faithfullyazi'll movements o f-ithe' con nected member frdmi the smallest t0 the greatest amplitude; For this reasonmy 'in-vention is highly efficient as a phonograph recording tool and-.515 a pickuporreproducer, especially forfthe new type of record in which the spiral jfik: runs t oi'sever'al hundred "lines to the me 2 Thesoperatidnhhd advantages of my'inventi'onwill be fully understood from a detailed description of the -ac'companying drawings, which show-"several forms electric phonograph "pickups constructed in 'accordance I 5 withzmyinvention." Iwanbi't clearly underfflhe essential 'featiire b f iny ini'entidn' "cbin'f prises ii'three-pol''inalgnet ii-nd a sprin arm; tn're" secured "zit" its" ends to thefiwo' onter ple'sl 0 armatu eisfgepamed fron the t hi rdlqr'in -f terinedi ate" niiignefi pole by in jairgqp; act l'iz ting member' is connected to the center stdod'th'at' I selected these partici lar embodimentsrnerely 'iby -way of example and not as restrlctlons or limitations of my inventien.

In thesedrawing's I f Fig.- 1 {shows an inside View of an electric pickup *aldaptedi for vertical cnt' records of the Edison typ'e'; with the stylus member mounted" directly on" the elastic armature;

2 is. *a' crossgsecticn 'on line 2-2 of Fig. 1 w]i th the'c'overplate onithe casing;

*Fig; 3' illustrates/a construction in "which the "stylus member is a pivQte'd n c'edle arfn connectd atyitsl'inner end toth'e armature springforplayi-ng lateralcut records; 5

Fig. 4 shows diagrammatically amodification "in which. the vibratory armature consists of) a ztensionecbmagnetic band or" ribbon stretched between' theoutr poles of a threepole'In et;'and w v 8 Fi'gu 5 is :a "fragmentary detail showing another way bf att-iiching'the armature band of Fig. 4 to the magnet pole:

-'=Beforeproceeding witha detailed description. of' the'=severalfiviews; I' wi'sh to explain thatwthe. drawings have been "made largely diagrammatic and I the parts have-been purposely exaggerated in their relative proportions sow-stomakethe figures'clear and easy to read. 5- The actual device is considerably smaller tl1ani.tl1eillustrations; which are therefore-not to 'be taken asshop drawings madet'o accurate scale. 1 I

nRQfBf-Iillg toEigsi Land 2, there is a casing 10 of nonmagneticmaterial, such as brass,

be a small light tube supported at its rearv end to allow movement of the reproducer over a record.

In casin 10 are mounted two permanent magnets 1 which are magnetically and mechanically connected to form a middle pole piece 18. If the polar ends 19 of the magnets are of north polarity, the pole piece 18 is of south polarity, as indicated in the drawings.

Rivets 20, or other fastening means, hold the two magnets together as a single structure, which is secured to the casing by bolts 21, or in any other practical way. As seen in Figs. 1 and 3, the magnets 17 follow generally the elliptic or oval outline of the casing, so that a magnetic path of maximum length is obtained in a small space. A coil 22 is mounted on the middle pole piece 18 and held thereon by any suitable means, as cross-pins 23. The coil is machine-wound and easily slipped in place after the magnets are connected.

The two magnets 17 are shaped from a flat bar of good magnetic steel, such as chromium or silicon steel, and they may be either solid or laminated. Since the two magnets are identical in shape, only one pattern or shaping device is needed. In this way it is possible to make the magnets from a long fiat bar which is bent at one end to form the curvedportion 19 and then the straight portion 18 is cut off for the right length. The complete magnet structure is made by simply connecting two magnets back-to-back.

The outer pole pieces 19 of the three-polar magnet structure 17 are connected by a spring armature 24, which consists of a magnetic leaf spring bent into the shape of an open ellipse. That is to say, the leaf spring is bent inwardly at its ends, as shown at 25, so that the central or main portion of the armature is suspended under tension between the curved ends of the spring for vibratory movement in its own plane. Suitable fastening members, such as bolts or rivets 26, secure the armature to the polar ends 19 of the magnet. The armature is in good magnetic contact with the pole pieces 19, and constitutes in effect an elastic vibratory extension thereof. The spring armature 24 is so dimensioned as to have the proper amount of resiliency and sufficient cross-sectional area to carry the tielrl flux without saturation.

In the broad aspect of my invention, any practical actuating member may be connected to the armature to vibrate the same in its own plane toward and from the central pole piece 18, from which the armature is always separated by a variable airgap 27. In Figs. 1 and 2 I have shown a stylus member 28 directly mounted on the armature spring 24 at or near the center thereof opposite the end of pole piece 18. The stylus member ,28 extends through an opening 30 in the bottom of casing 10. In this instance I have assumed that the stylus member 28 is intended to play vertical-cutrecords of the Edison type, which are usually played with a diamond point permanently attached to a suitable holder. In Figs. 1 and 2 a cross-sectional fragment of a vertical-cut record is diagrammatically indicated at 29.

The operation ofthe instrument above de-.

scribed will be plain to those skilled .in the art, but it might be well to summarize it in.

a few sentences: As the stylus member 28 moves up and down in accordance with the hill-and-dale variations of the record groove tracked by the stylus point 21, the elastic tensioned armature 24 vibrates in its own plane and varies the airgap 27. That is to say, when the stylus member 28 moves up, it pushes the armature closer to pole piece 18. The tension of armature24 is such that'it automatically springs away from pole piece 18 when the record groove permits. The flux variations thus produced in the field magnet system generate current impulses in the circuit of coil 22. Sincethe stylus member 28 is directly mounted on the armature spring 24, the stylus vibrations are transmitted to the armature Without lostvmotion, so that the minutest movements of the stylus point are faithfully converted into current impulses i n coil 22. The elliptic spring 24 responds correctly to all frequencies within audible range, because various lengths of the spring come into operation at different bands of frequencies. Thus, at high frequencies the central portion of the armature will vibrate. At low frequencies, the vibrating portion of the armature extends to the curved re silient ends 25, between which the central part of the armature is suspended. In other words, between the highest and lowest frequencies, different lengths or sections of armature spring 24 will respond instantly and faithfully.

I have not considered it necessary to show any circuit arrangement for coil 22, because amplifying circuits are well known in the electric phonograph and radio art. It is a simple matter to amplify the feeble current impulses in coil 22 by means of radio tubes for controlling or operating loudspeaker mechanism. This is so well understood that I need not say any more about'it. In the broad view 'of my invention, the current im- I when the stylus point 31 rests on a record,

the center of armature 24 is separated from the end of pole piece 18 by a small airgap, which is shown at 27 in exaggerated width. The elastic armature has sufficient inherent stiilness to take up the load of the reproducer without hitting the end of pole piece 18.

It is not necessar that the stylus member 28 should be directify mounted on the armature spring 24. For instance, referring to Fig. 1, it is easy to see that the stylus member 28 can be mounted at one end of a pivoted arm or lever which is connected at its other end to the center of the armature. In that way, the vertical movements of the stylus member 28 can be transmitted through thepivoted lever to the armature in amplified ratio. This will be understood without the need of additional illustration.

Fig. 3 differs from Fig. 1 in that the stylus mem er 28 of Fig. 1 is replaced by a needle arm 32 pivoted to the casinglO at 33 for playing lateral-cut records of the well-known Victor type. The needle arm 32 is connected at its inner end 34 to the center of armature spring 24, and the lower, end 35 of the needle arm is in the form of a holder for needles 36. The fragment 37 is supposed to represent a lateral-cut record in substantially radial cross-section. The casing 10 is mounted on the supporting arm 16 so as to hold the needle arm 32in proper playing position. A hole or slot 32 in casing 10 allows free movement of the needle arm. A simple way of mounting the needle arm on the casing is to provide the latter with a pair of ears 10' between which the pivot 33 is mounted. A pair of pointed screws mounted in the bearing lugs 10"are usually sufiicient to form a pivot support with practically no lost motion.

, It is evident fromFig. 3 that the vibrations of the needle arm 32 right and left pull and push the center of armature spring 24 away from and toward the face of pole piece 18. Otherwise,what has been said about the construction and operation of Fig.1, applies fully to Fig. 3 without the need of repetition. It will be noticed in Fig. 3 that the movements of the needle point 36 are transmitted in slightly amplified ratio to the armature 24.

In the modification of Fig. 4, the armature 38 consists of a steel band or ribbon having transverse corrugations 39 and secured at its ends to the outer'pole pieces 19 by magnetic pins or screws 40, or otherwise. The corrugations 39 hold the central portion of the armature band 38 in permanently stretched or tensioned condition, so that the armature will operate in substantially the same way as the elliptic spring 24 of Figs. 1 and 3. Otherwise, what has been said for Figs. 1 and 3 applies to Fig. 4, which will therefore be fully understood without further description.

Fig. 5 shows another way of attaching the ends of armature 38 to the outerpole pieces of the magnet structure. In this instance, each end of the tensioned armature ribbon carries a magnetic bracket 41, which fits tightly over the end of the magnet pole and is held in place by the bolt or rivet 42. This establishes good magnetic contact between magnet and armature.

It is hardly necessary to add that the constructions above described are equally adapted to operate as receivers, since current impulses in coil 22 will produce corresponding vibrations of armature 24 or 38, and these armature vibrations may be utilized in any practical way, as, for example, operating a recording tool or an acoustic diaphragm, vibrating a mirror that controls a photoelectric element, etc. Being constantly under tension, the leaf springs 24 and 38 are self-damping and respondinstantly and accurately whether the instrument acts as a transmitter or receiver. Should the armature spring accidentally be forced against the magnet pole 18, its own resiliency will cause it to recoil almost instantly, for the tension of the spring is stronger than the attractive force of the magnet at that point.

The three-pole magnet structure in this instrument need not be so heavy as the bipolar magnets in prior pickups usin a pivoted armature, where there is always Tost motion and where the low efficiency of the instrument requires an unusually heavy magnet. Those heavy pickups are also objectionable because they produce loud needle noises and tend to slow up the turntable. Attention is called to the fact that my three-polar magnet system provides a magnetic path of unusual length, thereby increasing the life of the magnetic field and the sensitivity of the instrument. The parts comprising my new instrument are few and cheaply made, are easily assembled and not liable to get out of order. The magnet and the parts carried thereby are inserted as a unit in the casing, where they are fully exposed for easy access by simply removing the cover 12. It is thus seen that I provide an electromagnetic transmitter and receiver of unusual simplicity and efficiency.

Although I have shown and described certain specific constructions by way of example, I want it understood that theillustrations in the drawings do not impose any restrictions or limitations as to details unless so specified in the claims that define my invention. Those claims which describe a phonograph reproducer are also intended to apply to a phonograph recording tool, since the same structure may be put to either use.

I claim as my invention: p

1. An electromagnetic device free from an lily acoustic diaphragm comprising a three-pole magnet structure in which the two outer poles are of like. polarity, a non-acoustic vibratory armature magnetically connected to said outer poles and separated by a variable airgap from the middle pole of said magnet structure, said armature consisting of an elastic band rigidly supported at itsends so that its main or central section is held under tension, and a coil operativcly associated with said magnet structure to cause vibration of said armature by electric impulses or to produce electric im pulses by the vibrations of said armature.

2. An electromagnetic device free from an acoustic diaphragm comprising a three-pole magnet structure in which the two outer poles are of like polarity, a non-acoustic spring armature magnetically connected at its ends to said outer poles, said armature consisting of an elastic band rigidly supported at its ends so that its main or central portion is held under tension, the central portion of said armatur being separated from the midd lepole of said magnet structure by an airgap,

an operating member connected to said armature at or near the middle thereof, and a coil arranged to produce electric impulses by the vibration of said armature or to actuate said armature in accordance with current impulses in the coil.

' 3. An electromagnetic device free from an acoustic diaphragm comprising a three-pole magnet structure in which the two outer poles are oflike polarity, a non-acoustic spring armature magnetically connected at its ends to said outer poles, said armature consisting of an elasticcband rigidly supported at its ends so that its main or central portion is held under tension, the central portion of said armature being separated from the middle pole of said magnet structure by an airgap, an operating member connected to said armature at or near the middle thereof, and a'coil' mounted on said middle pole.

4. An electromagnetic device free from an acoustic diaphragm comprising a three-pole magnet structure in which the two outer poles are of like polarity, an armature consisting of a flat spring bent inwardly at'the ends which are secured to said outer poles, whereby the central portion of said armature is resiliently supported'under tension by said curved ends for vibratory movement, the middle pole of said magnet structure being separated from the vibratory central portion of said spring'armature by an airgap, an operating member connected to said armature at or near the middle thereof, and a coil arranged to produce electric impulses by the vibration of said armature or to actuate said armature in accordance with current impulses in the coil. v

5. An electromagnetic device free from an acoustic diaphragm comprising a three-pole magnet structurein which the two outer poles are oi like polarity, an armature. consisting of a flat spring in one piece bent inwardly at the ends which are secured to said outer poles, I

whereby the central portion of said armature is resiliently supported by said curved ends for vibratory movement, the middle pole of said magnet structure terminating out of line with the outer pole pieces and being separated from the vibratory central portion of said spring armature by an airgap, an operatlng member connected to said armature at or near the middle thereof, and a c011 on sa d middle pole.

6; In an electromagnetic device free from an acoustic diaphragm, a magnet structure consisting of a pair of substantially U-shaped magnets having two like polar limbs connected together to form a middle or intermediate pole'piece, the other polar limbs of; said magnets c'oustituting'two outer polev pieces of like polarity, an elastic magnetic strip secured to said outer pole pieces and separated from said middle pole piece by an airgap, said elastic strip being held between its ends under tension and constituting a nonacoustic vvibratory armature to vary said airgap, and a coil on said middle pole piece.

7. In an electromagnetic device free from an acoustic diaphragm, a magnet structure consisting of a pair of substantially U-shaped magnets having two like i polar limbs con-f nected togetherto form a middle or intermediate pole piece, the otherpolar limbs of said magnets constituting two other pole piecesof like polarity, an armature consisting of a flat spring in one piecejbent inwardly at the ends which are secured to said outer poles, whereby the central portion ofsaid armature is resiliently supported by said curved ends for vibratory movement, the middle pole of said magnet structure being separated from the vibratory central portion of,

said spring armature by an airgap, said magnets and armature lying in the same plane, and a coil in operative relation to said magnets and armature.

8. An electric phonograph reproducer comof, and a coil associated with said magnet structure for converting the vibrations of said stylus member into electric impulses.

9. An electric phonograph reproducer free Ill] from an acoustic diaphragm comprising a i three-pole ma et in which the two outer poles are of'li (e polarity, an armature. consisting of a flat spring in one'piece bent inwardly at the ends which are secured to said outer poles, whereby, the central portion of said armature is resiliently supported by said curved ends for vibratory movement, .the middle pole of said magnet structure being separated from the vibratory central portion of said spring armature by an airgap, a stylus member connected to said armature at or near the middle thereof, and a' .coil associated with said magnet structure thereby, so that the vibrations of said stylus member are directly transmitted to said elastic armature to vary said airgap, and acoil for converting the vibrations of said stylus member-into electric impulses.

ADOLPH A. THOMAS.

for converting the vibrations of said stylus member into electric impulses.

10. In an electric phonograph reproducer 5 free from an acoustic diaphragm, a magnet structure consisting of a pair of substantially -U-shaped magnets having two like polar limbs connected together to form a middle or intermediate pole piece, the other polar limbs of said magnets constituting two outer pole pieces of like polarity, an elastic magnetic strip secured at its ends to said outer pole pieces and supported thereby, said elastic strip being separated from said middle pole piece by an airgap and constituting a tensioned vibratory armature to vary said airgap, a stylus member connected to said armature strip for actuating the same, and a coil for converting the movements of said armature strip into electric impulses.

11. In an electric phonograph reproducer free from an acoustic diaphragm, a magnet structure consisting of a pair of substantially U-shaped magnets having two like polar 3 limbs connected together to form a middle or intermediate pole piece, the other polar limbs of said magnets constituting two outer pole pieces oflike polarity, an armature consisting of a flat spring in one piece bent inwardly at the ends which are secured to said outer poles, whereby the central portion of said armature is resiliently supported by said curved ends for vibratory movement, the middle pole of said magnet structure being separated from the vibratory central portion of said spring armature by an airgap, a stylus member for actuating said armature, and a coil on said middle pole piece for converting the movements of said armature into current impulses.

12. An electric phonograph reproducer for playing vertical-cut records, comprising.

as I 

